fix: 7 bugs from multi-agent debug review of SQL layer

- Column name deduplication after sanitization (Score-A/Score_A collision)
- _safe_str() preserves None in Stata/SPSS/R data loaders
- Reject inf/Infinity in column type inference
- Guard against n=1 in _get_sample_values (ZeroDivisionError)
- NULL values render as "N/A" in SQL context (not "None")
- Defensive .get() in build_schema_summary for malformed schema
- Backtick-quoted table names in _extract_table_from_query regex

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/retriever.py

@@ -139,7 +139,7 @@ def build_combined_context(
 
 def _extract_table_from_query(sql_query: str) -> str:
     """Extract the first table name from a SQL query (best-effort)."""
-    match = re.search(r'\bFROM\s+"?(\w+)"?', sql_query, re.IGNORECASE)
+    match = re.search(r'\bFROM\s+["`]?(\w+)["`]?', sql_query, re.IGNORECASE)
     return match.group(1) if match else ""
 
 

src/sql_ingest.py

@@ -53,7 +53,10 @@ def _infer_column_type(values: list) -> str:
     # Try REAL
     try:
         for v in non_empty:
-            float(str(v).strip())
+            f = float(str(v).strip())
+            # Reject inf/nan — these are not valid REAL data
+            if not (-1e308 < f < 1e308):
+                raise ValueError("non-finite float")
         return "REAL"
     except (ValueError, TypeError):
         pass
@@ -84,6 +87,8 @@ def _get_sample_values(values: list, n: int = 5) -> list:
         sorted_vals = sorted(unique)
     if len(sorted_vals) <= n:
         return sorted_vals
+    if n <= 1:
+        return [sorted_vals[0]]
     # Pick evenly spaced indices including first and last
     indices = [round(i * (len(sorted_vals) - 1) / (n - 1)) for i in range(n)]
     return [sorted_vals[i] for i in indices]
@@ -348,12 +353,19 @@ def _load_rows_from_excel(file_path: str, ext: str) -> list[tuple]:
         return results
 
 
+def _safe_str(v):
+    """Convert a value to string, preserving None for missing data."""
+    if v is None:
+        return None
+    return str(v)
+
+
 def _load_rows_from_stata(file_path: str) -> list[tuple]:
     """Load Stata .dta into (None, headers, rows) tuples."""
     import pyreadstat
     df, _meta = pyreadstat.read_dta(file_path)
     headers = list(df.columns)
-    rows = [[str(v) for v in row] for row in df.values.tolist()]
+    rows = [[_safe_str(v) for v in row] for row in df.values.tolist()]
     return [(None, headers, rows)]
 
 
@@ -362,7 +374,7 @@ def _load_rows_from_spss(file_path: str) -> list[tuple]:
     import pyreadstat
     df, _meta = pyreadstat.read_sav(file_path)
     headers = list(df.columns)
-    rows = [[str(v) for v in row] for row in df.values.tolist()]
+    rows = [[_safe_str(v) for v in row] for row in df.values.tolist()]
     return [(None, headers, rows)]
 
 
@@ -373,7 +385,7 @@ def _load_rows_from_rdata(file_path: str) -> list[tuple]:
     tables = []
     for name, df in result.items():
         headers = list(df.columns)
-        rows = [[str(v) for v in row] for row in df.values.tolist()]
+        rows = [[_safe_str(v) for v in row] for row in df.values.tolist()]
         tables.append((name, headers, rows))
     return tables
 
@@ -487,6 +499,15 @@ def _ingest_tables(
 
             # Infer column types, collect samples and stats
             safe_headers = [_sanitize_column_name(h) for h in headers]
+            # Deduplicate: append _2, _3, etc. for collisions
+            seen: dict[str, int] = {}
+            for i, name in enumerate(safe_headers):
+                lower = name.lower()
+                if lower in seen:
+                    seen[lower] += 1
+                    safe_headers[i] = f"{name}_{seen[lower]}"
+                else:
+                    seen[lower] = 1
             col_types = []
             col_samples = []
             col_stats = []

src/sql_retriever.py

@@ -103,7 +103,9 @@ def format_sql_results_as_context(
             parts.append("")
 
     for i, row in enumerate(rows, 1):
-        fields = ", ".join(f"{k} = {v}" for k, v in row.items())
+        fields = ", ".join(
+            f"{k} = {v if v is not None else 'N/A'}" for k, v in row.items()
+        )
         parts.append(f"[CHUNK-SQL-{i:03d}] {fields}")
     return "\n".join(parts)
 
@@ -162,7 +164,8 @@ def build_schema_summary(schema: dict) -> str:
                 quoted = ", ".join(f'"{s}"' for s in samples[:5])
                 sample_str = f" e.g. {quoted}"
 
-            line = f"    {c['name']} ({meta_str}){sample_str}"
+            col_name = c.get("name", "unknown")
+            line = f"    {col_name} ({meta_str}){sample_str}"
             if desc:
                 line += f" \u2014 {desc}"
             lines.append(line)